Python codecov package is gone, breaks appveyor-coverage build

[mwichmann]

The codecov package has been removed from PyPI and fails the build:

if %COVERAGE% equ 1 .\.appveyor\install-cov.bat
Collecting coverage
  Using cached coverage-6.2-cp36-cp36m-win32.whl (182 kB)
ERROR: Could not find a version that satisfies the requirement codecov (from versions: none)
ERROR: No matching distribution found for codecov
Command exited with code 1
if ($env:COVERAGE -eq 1) { .\.appveyor\coverage_report.ps1 }

This was entirely intentional on the part of the company providing the package, and we have to seek alternatives.

https://about.codecov.io/blog/message-regarding-the-pypi-package/

Perhaps it's a good time to move a coverage build to a GitHub action, since one of the proposed mitigations from that blog is already available as a prebuilt action.

[mwichmann]

Updating - the one AppVeyor job that did codecov now no longer does; we have no replacement yet. Supposedly we can use this:

https://github.com/codecov/codecov-action